Polymers have been provided by nature in abundance and in a range of forms from biopolymers including polysaccharides such as cellulose to proteins such as collagen, each biopolymer able to undergo processes according to its own properties.
There are a number of methods in the art for modifying biopolymers, these include e.g. introduction of an aldehyde group into a protein, peptide or oligo through an amine reactive agent, or through diol oxidation, introduction of sulfhydryl groups through disulfide bond reduction and introduction of thiol groups by amine modification. Modifications involving the formation of ether groups are disclosed in U.S. Pat. Nos. 3,553,194 and 4,358,587. A treatment of viscose is disclosed in the Soviet publication SU 912,729, the formation of amide bonds is disclosed in U.S. Pat. No. 6,508,958 and a modified starch is disclosed in Chinese publication CN 102,311,554.
Many of these biopolymers are scarcely soluble in traditional molecular solvents such as apolar or polar organic solvents and thus modification is difficult and carried out under extreme conditions aided by prohibitively expensive and often toxic catalysts, such as cobalt, chromium, cerium, mercury, nickel and tin, which are all elements of high concern. However, it has recently been shown that lignocelluloses can be successfully dissolved in ionic liquids, cf. Haibo Xie, Ilkka Kilpeläinen, Alistair King, Timo Leskinen, Paula Järvi, and Dimitris S. Argyropoulos, “Opportunities with Wood Dissolved in Ionic Liquids” in Tim F. Liebert, Thomas J. Heinze, Kevin J. Edgar (ed.) Cellulose Solvents: For Analysis, Shaping and Chemical Modification ACS Symposium Series, Volume 1033 (2010), p. 343-363.